Field of the Invention
The present invention relates to a field-effect transistor having a contact to one of its doping regions, and to a method for fabricating it.
In the technical field of semiconductor components, such as for example field-effect transistors, it is customary and necessary to produce an electrical contact to a doped region that is disposed in a semiconductor substrate. By way of example, if two adjacent gates of two adjacent field-effect transistors are disposed next to one another on the surface of a semiconductor substrate and a doping region is disposed between the two gates in the semiconductor substrate, it is known to line the two gates on their surfaces and side walls with a liner as an etching mask, in order to form a self-aligned contact to the doping region between the two gates. By way of example, U.S. Pat. No. 5,908,791 discloses a device with a gate electrode and a layer of WSi (tungsten silicide).
The cladding of the two gates is typically formed from silicon nitride, and the gates are typically formed from polycrystalline silicon. The gates and the substrate are usually covered with a silicon oxide in which contact holes are disposed. The etching selectivity between the layer of silicon oxide and the liners made from silicon nitride is used to form the contact holes. By way of example, the mask which is used to pattern the contact holes between the two gates may be misaligned, so that a contact hole which is subsequently etched using the patterned etching mask would be formed not only between but also into a gate. This is usually prevented by the liners, which contain silicon nitride, wince the etching of the contact holes through the liners, which have a significantly lower etching rate than the silicon oxide, is directed between the two gates, the two gates being protected from the contact-hole etching by the liner containing silicon nitride.
However, a drawback of the prior art is that during the etching of the contact holes material is also removed from the liner formed around the gate, so that holes may form in the liner, and may lead to damage to the gate and/or to a short circuit between the gate and a contact plug which has been introduced into the contact hole.